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Omphalosaurus
Since the genus was first named from fossils in Nevada, USA, Omphalosaurus was usually perceived as a small and primitive ichthyosaur that lived during the early Triassic. Towards the end of the twentieth and early twenty-first centuries however questions were raised about the genus being an ichthyosaur with notes about how the known fossils of Omphalosaurus don’t show any feature that are exclusive just to the ichthyosaurs. Most of this doubt was highlighted in a paper by Motani and published in 2000, however since this papers by Sander and Faber in 2003, and Maisch in 2010, both describing new specimens of Omphalosaurus, have concluded that Omphalosaurus is a primitive ichthyosaur. One thing that we can be a little more certain about Omphalosaurus is the diet.‭ ‬The teeth of Omphalosaurus are blunt and rounded,‭ ‬and usually these kinds of teeth are seen in animals that eat hard bodied items.‭ ‬In reference to Omphalosaurus specifically this would be shellfish which would have had their hard outer shells broken up by the teeth so that the soft inside could then be swallowed by the feeding‭ ‬Omphalosaurus. Omphalosaurus is an extinct genus of marine reptile from the Middle Triassic. It has generally been considered anichthyopterygian until Motani showed that it lacks the basal synapomorphies of Ichthyopterygia. However, Maisch described a new species and restated its affinity with Ichthyosauria. Several species of Omphalosaurus have been described from the western United States, Germany, and the island of Spitsbergen off the northern coast of Norway. Known from only a few scraps plus a few skull pieces that few paleontologists can confidently identify, Omphalosaurus has baffled workers for over a hundred years. Considered “aberrant and fragmentary” by Maisch, Omphalosaurus as been nested in and out of the Ichthyopterygia because there are no closely related sister taxa. It really is ‘out there,’ pretty much all alone. Meriam erected the genus based on a fragmentary skull with two associated vertebrae from the middle Triassic of Nevada. He considered it a distinct sort of reptile possibly related to placodonts or rhynchosaurs based on the button-like and disordered dentition. Shortly thereafter, Wiman described similar teeth form the Lower Triassic of Spitzbergen. The postcranial bones included discoidal vertebrae and humeri that resembled those of the ichthyosaur, Shastasaurus. Wiman erected a new genus and three species based on fragmentary remains. Later papers by both workers split the fossil generically, considering the vertebrae ichthyopterygian, and the dentition something else. More recent papers lumped Omphalosaurus with the ichthyosaur, Grippia, typically without citing reasons for doing so. Mazin stated reasons for including Omphalosaurus within the Ichthyopterygia. Tichy described a more complete specimen from Austria. Sander and Faber added data to this enigma. The holotype is difficult to interpret, according to Motani. The key feature of Omphalosaurus is the presence of rounded teeth that do not form a single tooth row, but are established, almost randomly, along the premaxilla and dentary. The maxilla appears edentulous. The extent of the splenials is also unmatched, including an elongated symphysis. Motani concluded that the Wiman Spitzbergen material consisted of several distinct genera. Motani nested Omphalosaurus outside of the Ichthyopterygia, more basal than Utatsusaurus. This is always a problem nesting enigmas at the base of any clade without including further outgroups. The great extent of the splenial is a key trait when looking for the closest known sister taxon. Fortunately this trait is extremely rare, virtually unknown elsewhere within the Reptilia. Look for any other marine taxa that has a greatly extended/expanded splenial and you are left with just two taxa that were not previously considered in any discussions of Omphalosaurus. While Sinosaurosphargis is clearly greatly derived with a turtle-like shell and and Largocephalosaurus is not so derived, these are the only other taxa with an extensive set of splenials that form a symphysis anteriorly, brief though it may be. The teeth are not so derived. The ribs were not so derived. Even so, the splenials were similar. So were other skull bones, like the much greater width of the premaxillae compared to the dentaries. And when you’re dealing with an enigma like Omphalosaurus, so different from any other fossil currently known, you grasp at straws. Others have not attempted to match these taxa to Omphalosaurus. Category:Mravid Category:Ichthyosaurs Category:Triassic Category:Triassic reptiles